1. Field of the Invention
This invention relates to an apparatus for sterilizing a water-soluble lubricant used in various machining works.
2. Description of the Prior Art
In many cases, machining works have been done using water-soluble lubricants such as water-soluble cutting oils and water-soluble grinding oils in a grinding or cutting machine. Water-soluble lubricants can be recycled after being purified. In other words, after removal of metal flakes contained in the water-soluble lubricant discharged from a machining apparatus, the lubricant is fed into a tank and then returned to the apparatus for reuse.
Microorganisms and bacteria are prone to proliferate in a water-soluble lubricant circulation system which is open to the air because the lubricant is kept at an increased temperature due to heats developed during machining operations or resulting from an increased atmospheric temperature during the summer season. The proliferated microorganisms cause the lubricant not only to emit rancidity and but also to be reduced in pH. Such pH reduction causes the lubricant to change in appearance such as deteriorated emulsion stability, oil-water separation and discoloration (black), and to be reduced in rust preventing properties and lubricity. For example, it is known that when the colony forming unit in a water-soluble lubricant exceeds 105 to 106 units per milliliter, the lubricant emits rancidity which is originated from anaerobic bacteria. For the purpose of preventing the rancidity emission, sterilizers and antiseptics have been added to a lubricant every few weeks or every time the machining operation is temporarily terminated such as on holidays. Alternatively, some countermeasures have been taken by modifying equipment, such as methods of aerating the tank of a circulation system, blowing steam, spraying an ozone-containing gas, irradiating ultrasonic waves, radial rays or ultraviolet rays and adding a metal cation such as silver ion and copper ion, to the tank. These methods are disclosed in Japanese Patent Laid-Open Publication Nos. 56-95992, 60-115697, 63-245494, 2-212597, 4-264199, 62-215507, 2-29496, 5-230492 and 9-135885, respectively.
However, the use of sterilizers is disadvantageous in that its effects last a short time and it is harmful to the human body. The spraying air or steam is inconvenient in that it is less effective in suppressing the proliferation of microorganisms and is not sufficient in view of long lasting effect. The method of spraying an ozone-containing gas or irradiating radial rays or ultrasonic waves is also disadvantageous in that it adversely affects the emulsion stability of a lubricant to be denaturalized, leading to loses in inherent properties thereof and also increases the costs of facilities and operations. Similarly, the method of irradiating ultraviolet rays and adding a metal cation also suffers the same problem that it is less effective in suppressing the proliferation of microorganisms and causes the elevated equipment and operation costs. Therefore, any of these conventional methods can not be a sufficiently effective measure because of the influence on a lubricant and in an economical view.
A method of sterilizing an aqueous solution is generally known in which a voltage is applied to the solution using electrodes. However, an application of this method to a water-soluble lubricant causes the lubricant not only to lose its inherent performances, resulted from changes in the quality of additives contained therein by an electrical oxidation-reduction reaction but also to be reduced in pH facilitated by hydrogen cations generated when applying a voltage. As a result of this, microorganisms are prone to proliferate.
In view of the foregoings, the object of the present invention is to provide a sterilization apparatus which can perform a stable sterilization of microorganisms and suppress the proliferation thereof, with economical advantages.
The present inventors applied the hydrogen peroxide on-site formation technology to the present invention. More specifically, it is generally known that the application of a faint voltage using carbon electrodes brings about the following reaction at the cathode, thereby forming a hydrogen peroxide anion, as described in xe2x80x9cKagaku Kogakuxe2x80x9d, vol. 51, No. 6, p 417-419 (1987), written by Masao Sudo.
O2+H2O+2exe2x88x92xe2x86x92HO2xe2x88x92+OHxe2x88x92xe2x80x83xe2x80x83(1)
As disclosed in Japanese Patent Laid-Open Publication No. 61-284591, it is also known that application of a voltage to a cathode chamber in the presence of a redox compound or resin (Q) causes the turn over of the following reactions.
Q+nH++nexe2x88x92xe2x86x92HnQxe2x80x83xe2x80x83(2)
HnQ+(n/2)O2xe2x86x92Q+(n/2)H2O2xe2x80x83xe2x80x83(3)
Furthermore, it is known that when a voltage is applied using a cathodic electrode supporting thereon an electrically conductive polyaniline, the following reactions progress in a cycle, thereby forming hydrogen peroxide as described in Chem. Lett. 1996, p 615, by K. Morita et. al. or ibid, vol. 15, No. 5 (1997).
PA+nH++nexe2x88x92xe2x86x92HnPAxe2x80x83xe2x80x83(4)
HnPA+(n/2)O2xe2x86x92PA+(n/2)H2O2xe2x80x83xe2x80x83(5)
However, when anodic and cathodic electrodes are immersed into a water-soluble lubricant and the application of a voltage is continued in order to utilize the above-mentioned reactions, protons generated from the anodic electrode by the following reaction mechanism reduce gradually the pH of a lubricant.
2H2Oxe2x86x92O2+4H+4exe2x88x92xe2x80x83xe2x80x83(6)
Such pH reduction deteriorates the rust-preventing performances and lubricity of a lubricant and moreover facilitates the proliferation of microorganisms, resulting in an extremely shortened sterilizing effect. Furthermore, an reaction-oxidation reaction always progress on the anode, accompanied with the oxidation decomposition of additives contained in a lubricant. After an extensive research and study, it has been found that the foregoing problems can be solved by isolating an anodic electrode with a diaphragm such that protons hardly flows into the water-soluble lubricant and also the lubricant is avoided from being changed in quality.
According to the present invention, there is provided a sterilizing apparatus which comprises a container, an anode and a cathode arranged therein and supplied with a voltage and a partition arranged so as to divide the container into a cathode section into which a water-soluble lubricant is introduced and an anode section into which an electrically conductive material is introduced and provided at least partially with a diaphragm such that an electric current flows between the anode and the cathode and such that the cathode generates a substance sterilizing the lubricant.
The cathode forming the sterilizing substance is preferably a carbon-based electrode.
The cathode forming the sterilizing substance is preferably an electrode supporting an organic compound having an oxidation-reduction capability.
The cathode forming the sterilizing substance is preferably an electrode supporting a redox resin.
The cathode forming the sterilizing substance is preferably a carbon-based electrode or an electrode supporting an organic compound having an oxidation-reduction capability.
The cathode forming the sterilizing substance is preferably a carbon-based electrode or an electrode supporting a redox resin.
The cathode forming the sterilizing substance is preferably a carbon-based electrode or an electrode supporting an organic compound having an oxidation-reduction capability or supporting a redox resin.
The organic compound having an oxidation-reduction capability is preferably benzoquinone, naphthoquinone, anthraquinone or derivatives thereof.
The redox resin is preferably a quinone-based redox resin.
The redox resin is preferably polyaniline.
The cathode section is preferably provided with an inlet port through which a water-soluble lubricant is introduced and an outlet port through which a sterilized water-soluble lubricant is discharged.
The cathode section is preferably provided with a separator which separates impurities from a water-soluble lubricant with the specific gravity and contacting the separated lubricant with the cathode. The separator can prevent a machine oil and a sliding surface lubricant used in machining operations and floating the upper portion of the lubricant from adhering to the cathode and the diaphragm.
The electrically conductive material is preferably a buffer solution or an alkaline aqueous solution, so as to suppress changes in pH. The anode section is preferably provided with a stirrer such that protons generating from the electrode can be neutralized effectively when the electrically conductive material is charged into the anode section.
If the alkaline aqueous solution leaks from the anode section by some accident, it is very harmful to the human body. Therefore, the alkaline aqueous solution is preferably thickened or gelled as to be formed into a solid electrolyte by adding a thickening or gelling substance. The buffer solution may be thickened or gelled so as to be a solid electrolyte by adding a thickening or gelling substance.
A controlling circuit applying a voltage to the anode and the cathode is preferably provided with a circuit reversing the flow direction of the electric current temporarily. The reversing circuit makes it possible to remove contaminants formed over the surface of the electrode or the diaphragm and prevent the electric current from lowering if it happens.
When a water-soluble lubricant is continuously introduced into the cathode section, the sterilizing substance may not be accumulated in more than certain levels of concentration, on the cathode. This may cause a continuous state in the apparatus which fails to complete sterilization, leading to the proliferation of microorganisms and molds on the cathode during the operation. Finally, the efficiency of the sterilizing substance formed is extremely reduced. In order to accumulate temporarily a high concentration of the sterilizing substance in the cathode section so as to keep the section in a germfree condition, the container is preferably provided with a supplying means which can supply a water-soluble lubricant to the cathode section intermittently every and for a certain period of time.
In order to downsize the container, it is preferred to arrange two diaphragms such that one anode is located at the center of the space therebetween and to arrange two cathodes in sandwich relation to the two diaphragms.
As described above, in the present invention, since a cathode is an electrode forming substance sterilizing a water-soluble lubricant and is separated from an anode with a diaphragm, the protons forming from the anode is prevented from flowing into the lubricant and the sterilizing substance is free from decomposition by the anode, leading to sterilization of the lubricant in a stable manner.
Therefore, the present invention is also economically advantageous.